1. Related Field
The invention relates to a method and a machine for producing a structured fibrous web, in particular a tissue web. The fibrous web produced may be used as, for example, kitchen towel, toilet paper or facial tissue.
2. Description of Related Art
A machine for manufacturing structured soft paper is disclosed in U.S. Pat. No. 6,287,426. The machine disclosed in that patent has a forming section with a head box and two forming fabrics. The formed web is passed on a water receiving felt through a dewatering nip. An impermeable belt is also passed through the dewatering nip and the web is transferred to the impermeable belt. The impermeable belt then conveys the fibrous web to a wire 22 which has a web-contacting side with a structure. A suction device placed within the loop of the wire is used to pick up the web from the impermeable belt and transfer it to the structured wire. The web is then passed to a drying cylinder which may be a Yankee dryer. When the web is passed from the impermeable belt to the structured wire, a speed difference is used in order to achieve structuring. This means that the wire moves at a speed that is less than the speed of the impermeable belt. Such a speed difference is sometimes referred to as “rush transfer”. It is stated in that document that the speed difference can be 10-25%. While this machine may give a good result in terms of bulk, the inventor of the present invention has discovered that the paper web may sometimes be damaged. The inventor of the present invention has found that it is difficult to operate such an arrangement at speed differences larger than about 8%. When the speed difference is larger than about 8%, sheet transfer is often lost and the web is damaged. It is therefore an object of the present invention to reduce the risk that the paper web is damaged, even when the speed difference is larger than 8%.
U.S. Pat. No. 7,588,660 discloses another machine for manufacturing structured soft paper. In that patent, the formed web is transferred to a felt and passed through a single-felted dewatering nip in which the fibrous web is passed to a transfer roll. From the transfer roll, the web is passed through a nip to a creping fabric. Such an arrangement requires that three rolls cooperate which is difficult due to deflection of the rolls in the nips. Moreover, the creping wire may be subjected to wear as it contacts the transfer roll.
Another machine for producing paper webs is disclosed in U.S. Pat. No. 6,187,137, That document discloses how a wet web may be transferred first from the forming section to a first transfer fabric and from the first transfer fabric to a second transfer fabric which may be adapted to impart texture and bulk to the web, Transfer to the second transfer web may be done by means of rush transfer whereafter the web may be transferred to a cylindrical dryer.
Yet another machine is discussed in U.S. Pat. No. 5,830,321, In that patent, rush transfer is discussed and the transfer takes place when the fabrics involved pass over a vacuum shoe and a deflection element respectively.